In general, an autonomous vehicle (also referred to as an unmanned vehicle) is a vehicle capable of monitoring external information and recognizing a road situation and autonomously travelling to a set destination by itself without manipulation of a vehicle owner.
Further, due to a characteristic of a larger noise than a gasoline vehicle, a diesel vehicle using diesel as a fuel performs pilot injection control which causes deterioration of fuel efficiency for a silent and comfortable driving environment.
Here, the pilot injection decreases an ignition delay time of main injection by injecting fuel with a small time difference before the main injection for generating operation power of the vehicle to facilitate combustion. The pilot injection control injects a small amount of fuel before the main injection, so that fuel efficiency may slightly deteriorate, but noise and vibration of a diesel engine may be decreased through the decrease of fuel efficiency.
However, when an autonomous diesel vehicle is unmannedly operated, quiet driving by decreasing a noise of the diesel engine is meaningless because there is no passenger inside the vehicle, and this causes a problem in that fuel efficiency is unnecessarily degraded through the pilot control. Further, it is difficult for a pedestrian to recognize a vehicle when engine noise of the autonomous diesel vehicle is small, so that there is a problem in that a danger of an accident is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.